1. Field of the Invention
The present invention relates to an etchant for patterning a composite layer and a method for fabricating a patterned conductive layer of an electronic device using the same.
2. Description of Related Art
As the thin film transistor liquid crystal display (TFT-LCD) panel gets larger in size, the metal wires having significantly higher resistivity will result in resistance-capacitance (RC) delay. Consequently, signals are being distorted during transmission and the panel display quality is thus affected. Using metal wires made of copper, which has a significantly lower resistivity, may effectively reduce the effects of RC delay. Nonetheless, the adhesion between copper and glass substrate is rather weak and copper diffuses easily. Therefore, other metal such as molybdenum is used to be the adhesion layer to strengthen the adhesion between the adhesion layer and the glass substrate, which also acts as a barrier layer to prevent diffusion.
However, etching a composite metal layer is not easy. Usually, more than two etchants are required to achieve the etching of a composite layer in multiple-etching steps. Nevertheless, this method is somewhat time-consuming. The Galvanic effect is easily resulted if a pure copper etchant used frequently in the traditional package industry or a PAN acid used by the panel industry is used to perform etching, which will also lead to etching undercut, and it will be harder to control the etch rate. Subsequently, a desirable etching cannot be obtained. Another etchant, as described in U.S. Pat. No. 6,780,784, primarily comprises of hydrogen peroxide (H2O2). Nonetheless, the concentration stability of a H2O2-based etchant cannot be easily controlled. Further, a highly concentrated H2O2-based etchant will cause damages to the components of the machines and result in potential occupational hazards. Hence, there is a need for an etchant that may be used to etch metal conductive lines in a composite layer.